SPATIAL VARIABILITY OF INORGANIC NUTRIENTS IN THE MARGINAL ICE-ZONE OF THE BELLINGSHAUSEN SEA DURING THE AUSTRAL SPRING

Data on nutrients (nitrate, nitrite, ammonium, phosphate, silicate) bi ogenic-silica and chlorophyll a concentrations were collected along a south-to-north transect through the marginal ice zone of the Bellingsh ausen Sea during the Austral spring of 1992. There was a marked gradie nt in near-surface (less than or equal to 100 m) concentrations from t he most southerly occupied station (70 degrees 15'S, 85 degrees 07'W) to the northernmost (67 degrees 30'S, 85 degrees 00'W). Nitrate, phosp hate and silicate concentrations decreased along the transect from 33 to 21, 2.2 to 1.2 and 76 to 35 mmol m(-3), respectively. Nitrite, ammo nium and biogenic-silica levels increased from 0.04 to 0.16, 0.01 to 2 .5 and 0.2 to 4 mmol m-3, respectively from south to north. Chlorophyl l a concentrations increased from similar to 0.1 at the most southerly station to > 4.0 mg m(-3) in the north. A simple ice-melt model sugge sts that only a proportion of the previous winter's sea ice had melted in the study area. The impact of this ice-melt on nutrient concentrat ions was trivial. Predicted time-scales of nutrient removal by phytopl ankton growth varied for the three nutrients. Nitrogen uptake appeared to be underestimated with respect to phosphorous, consistent with mea surements of nitrogen preference from the same cruise. Silicate use ap peared to have started later than nitrogen or phosphorus uptake, indic ative of species succession in the phytoplankton. Hydrographic variabi lity accounted for some of the silicate change but not the nitrate or phosphate anomalies. In the case of both nitrogen and phosphorus utili sation, the duration of uptake for steady-stare growth at a rate of 0. 1 day(-1) appeared greater than that available in the interval between the start of the ice retreat and the time of the study.